This preliminary economic assessment evaluates a run-of-mine heap-leach processing route for gold and silver recovery from the Goldstrike mineralized material in southwestern Utah.
Report context
The Goldstrike Project is an early-stage gold exploration project located approximately 50 km northwest of St. George in Washington County, southwestern Utah, USA. Liberty Gold Corp., listed on the Toronto Stock Exchange (LGD), holds its interest through its indirect subsidiary, Pilot Goldstrike Inc. In February 2018, Liberty Gold commissioned SRK Consulting to undertake a preliminary economic assessment (PEA) for the Goldstrike Project, with services rendered from March to July 2018. The summary results were disclosed publicly by Liberty Gold in a news release on 10 July 2018. This PEA is partly based on a mineral resource statement prepared by Advantage Geoservices Ltd and reviewed by SRK.
Processing route
Recovery methods
The process selected for recovery of gold and silver from the Goldstrike mineralized material is a run-of-mine (ROM) heap-leach circuit. The material will be mined by standard open pit mining methods and truck-stacked onto heap leach pads in 9-meter (30-foot) lifts.
The ROM material will be leached with a dilute cyanide solution. Leached gold will be recovered from solution using a carbon adsorption circuit. Gold will be stripped from carbon using a desorption process, followed by electrowinning to produce a precipitate sludge. The precipitate sludge will be refined in a furnace to produce doré bars.
Heap leach facility
The planned heap leach facility (HLF) includes one dedicated lined leach pad and a lined process and event pond system designed to be constructed in three phases. The HLF site was selected as the preferred site out of six sites reviewed. The selected site is designed to hold approximately 60 Mt of leachable resource using a stacked dry density of 1.6 t/m³. Under the design criteria and assumptions used, the heap leach pad is designed to be stable to a maximum stacked height of 100 m. Shaping and grading of the site will use mine waste rock placed as engineered fill to construct a toe fill at the base of the leach pad and for a flat pad where the process pond, event pond, and process plant will be constructed.
Prior to final phase construction (Phase 3), the northeast side of the Moosehead Pit will be backfilled, and the Phase 3 leach pad liner is designed to be constructed over the backfilled pit to provide positive drainage of Phase 3 to the process ponds.
The leach pad and process and event ponds will be lined with geomembrane lining systems in accordance with current industry practices for ground water protection. The lined ponds will be sized to contain gravity solution flow during normal operating conditions in addition to severe emergency events including severe storm events and a power or pump outage that prevents recirculation to the desorption plant or back to the leach pad.
Off-site infrastructure
The mine is located proximate to major infrastructure. The major components of off-site infrastructure that have been considered are:
- An upgrade and partial realignment of the existing access road from Old Highway 91 to the mine site
- The installation of a high-voltage transmission line and associated sub-station along the access road alignment from a substation in the St. George area
- The provision of water supply from a bore-field to the mine site via a 9-km pipeline and associated pumping facilities, with the pipeline assumed to primarily follow existing roads
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Mining | ||
| Mining method | Standard open pit | Design |
| Total leach tonnes mined | 59.3 million tonnes | PEA plan |
| Total tonnes waste mined | 70.6 million tonnes | PEA plan |
| Tonnes per day mined | 22,500 tpd | Design |
| Strip ratio (waste:leach material) | 1.2:1 | PEA plan |
| Mine life | 7.5 years | PEA plan |
| Processing | ||
| Processing method | ROM heap-leach with carbon adsorption | Design |
| Heap leach lift height | 9 meters (30 feet) | Design |
| Heap leach pad capacity | ~60 Mt at 1.6 t/m³ dry density | Design |
| Maximum stacked height | 100 m | Design |
| HLF construction phases | 3 phases | Design |
| Gold recovery | 78% | PEA estimate |
| Production | ||
| Total gold ounces mined | 915,516 oz | PEA plan |
| Total gold ounces recovered | 713,004 oz | PEA calculation |
| Average annual gold production | 94,493 oz | PEA estimate |
| Peak annual gold production | 117,855 oz | PEA estimate |
| Head grade | 0.48 g/t | PEA estimate |
| Metallurgical testwork | ||
| Testing recommendation | Expand to untested areas (Peg Leg, Dip Slope, Moosehead, Beavertail, Covington) using large-diameter core | Recommendation |
| Additional testing recommended | Column residues and process solutions characterization for environmental permitting; blending of clayey material with coarser rock types; primary crushing and agglomeration testing | Recommendation |
Project website: https://goldstrike3d.com/
Technical qualifications
The economic analysis is partly based on inferred mineral resources that are considered too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves, and there is no certainty that the preliminary assessment based on these mineral resources will be realized. The level of accuracy of the capital cost estimate is approximately -20%/+40%. Operating costs were estimated with a level of accuracy of approximately -25%/+25%, which is appropriate for a PEA.
Source: Goldstrike PEA NI 43-101 Technical Report, July 2018, SRK Consulting.
